From Dark and Darker Wiki
Gingerbread cookies have a total drop rate for normal enemies of 0,45%: - 0,1% for 1 cookie - 0,1% for 2 cookies - 0,25% for 3 cookies
For elite bosses and mini-bosses or nightmare monsters it's 0,9% total: - 0,2% for 1 cookie - 0,2% for 2 cookies - 0,5% for 3 cookies